Nitriding serves to harden the surface of metal pieces.
Several hardening methods exist that are implemented in static environments, i.e. without significant motion. In particular, there is nitriding by means of gas, a bath of salts, powder, and by means of ion nitriding. More recently, a technique of ion implantation has been proposed.
Those methods enable a layer having a thickness of 1 to 2 tenths of a millimeter to be hardened on alloys of titanium.
There also exists a non-static method in which a laser beam that is movable relative to the piece is directed onto the piece and procures a small amount of surface melting in the impact zone, nitrogen is blown onto the piece in a direction that remains fixed relative to the direction of the laser beam, and an inert gas is also blown onto the piece(EP-A-0 491 075).
In that method, the nitrogen is mixed with the inert gas and both the laser beam and the nitrogen-inert gas jet converge on the piece so that the gaseous mixture strikes the liquid zone. To prevent said zone being converted into a spray, it is necessary to limit the pressure of the gas jet.
The above method has made it possible to obtain hardening over a thickness of 0.4 mm to 1 mm on a piece made of titanium alloy.